Overhaul concatenation and allow for correct concatenation of multiple overlapping datasets

[valeriupredoi]

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Closes #574

Summary

• continuation of the previous implementation of concatenation of two overlapping cubes
• handles corner case situations as @mwjury has noticed in concatenation of cubes with overlapping data #574
• fixed one bug in testing (that was due to bad implementation of the function in _io.py)

New Features

• handles a list of cubes to be concatenated of form [A, B, C, D...] with any sort of overlap in time between the cubes
• turns off iris's faulty automatic concatenation of eg [A, B, D] with a massive gap between B and D and inability of previous implementation to plug the gap with C
• if the cubes are [A, B, D, C...] and B and D don't have an overlap but C or later cubes overlap, it will still work

Tagline

• probably the mother of all concatenations we've ever had 😁

[valeriupredoi]

@bjlittle such an implementation would be nice to have in iris, this can easily be ported if you guys would be OK with it 🍺

[valeriupredoi]

@bouweandela @jvegasbsc cen we have a look at this pls, I suspect it's gonna be quite useful (@mwjury has already tested for his two used cases that were not working previously) 🍺

[bouweandela]

Nice improvement, but I think the implementation could still be simplified a bit. Could you have a look?

[valeriupredoi]

Nice improvement, but I think the implementation could still be simplified a bit. Could you have a look?

cheers @bouweandela you are correct - I have streamlined it now, have a looksee 🍺

[rswamina]

@valeriupredoi - I found that this was a problem with the NorESM2-LM dataset as well. I think the same fix will work. Happy to try out once this branch is merged with the master.

[bouweandela]

Nice work, could you please have a look at the comments?

[valeriupredoi]

all done, mi amigo @bouweandela 🍺

[bouweandela]

Thanks, looks good now! Just a tiny remark about the error message.

@mattiarighi Could you please test?

[valeriupredoi]

cheers @bouweandela - no need to test, @mwjury tested this in the issue, and meself included 🍺

[bouweandela]

Sorry, I forgot to ask about Codacy, could you have a look?

[valeriupredoi]

yeah Codacy can go for a walk 😁